PROJECT SUMMARY/ABSTRACT Neurotropic viruses are a significant cause of morbidity and mortality in children and adults. The central objective of this proposal is to enhance an understanding of mechanisms by which viruses injure the central nervous system (CNS). Mammalian reoviruses serve as highly tractable models for studies of neurotropic virus-host interactions. Reoviruses are neurotropic and highly virulent in young mammals. Like other neurotropic viruses, reovirus causes apoptosis in the murine CNS, leading to fatal encephalitis. However, it is not known if this pro-apoptotic capacity is a trait that benefits viral fitness, an inadvertent effect of host immune defense, or a combination of both. An important host determinant of reovirus-induced apoptosis is the innate immune transcription factor NF-kB. Reovirus neuropathology is attenuated in mice deficient in NF-kB, but the mechanism of NF-kB-mediated reovirus neural injury remains largely undefined. Three specific aims are proposed to elucidate the role of apoptosis in reovirus infection and enhance an understanding of cellular mechanisms mediating reovirus-induced apoptosis in the CNS. In Specific Aim 1, the role of apoptosis in reovirus infection will be defined. Isogenic mutant viruses with single amino acid changes that modulate apoptotic capacity will be engineered and compared for the capacity to replicate, disseminate, cause tissue injury, and transmit between hosts. In Specific Aim 2, the contribution of cell type-specific NF-kB signaling to reovirus-induced encephalitis will be determined. Neuron- and hematopoietic-specific NF-kB-deficient mice will be generated and infected with reovirus. Viral replication, dissemination, tropism, and tissue injury in these animals will be assessed. In Specific Aim 3, NF-kB-regulated mediators of reovirus-induced apoptosis in the CNS will be identified using an in vivo imaging mass spectrometry approach. Candidate proteins will be analyzed using models of reovirus cell injury and neuropathology. These studies will provide important insights into mechanisms of viral disease in the CNS and may lead to the development of novel strategies for therapeutic intervention.